1. Field of the Invention
This invention relates to a zoom lens for use in a TV camera or the like.
2. Related Background Art
The zoom portion of a zoom lens can be controlled to move the lens position to thereby increase or decrease the photographing angle of view, but when the focus position of the zoom lens is controlled, the lens position is likewise moved, whereby the angle of view is varied. That is, even if a desired angle of view is set by the zoom portion, the set angle of view is fluctuated by the control of the focus portion. Therefore, there has been proposed a zoom lens having the so-called angle of view fluctuation correcting function of controlling the zoom portion so that any fluctuation in the angle of view may not occur when the focus portion is controlled.
FIG. 10 of the accompanying drawings shows a flow chart of the zooming operation including the angle of view correcting operation in a zoom lens of a type which controls the position of the lens. In this zoom lens, data are inputted from zoom demand and focus demand (steps 53 and 54), and when there is the input of data from focus demand, a zoom command position for angle of view fluctuation correction is calculated (steps 58 and 61). On the basis of the result of this calculation, a motor for driving the zoom portion is driven (step 62).
Now, some of zoom lenses have the function of limiting the driving range of the zoom portion (the so-called tracking function). In the zoom lens of which the wider angle of view and higher magnification are progressing year by year, when the zoom portion is set to the wide-side, even a person or persons or the like around an object to be photographed who are not wanted to be photographed may come into the image field, and on the other hand, when the zoom portion is set to the tele-end, the object to be photographed may be too much enlarged to be contained in the image field. In such a situation, the operator of the lens needs always to delicately adjust the zoom stop positions on the wide-side and the tele-side by zoom demand.
So, the tracking function for making it possible to limit the driving range of the zoom position, photographing only and object to be photographed at the wide-end and photographing such an image that the whole image of the object is surely contained in the image field at the tele-end without effecting the delicate adjustment by zoom demand becomes useful.
Also, some of zoom lens apparatuses have, in addition to the above-described tracking function, the function of limiting the driving range of the zoom portion (the so-called F value preferred function) in order to avoid the so-called F drop phenomenon that the brightness of the image field is reduced by the driving of the zoom portion. Although in the zoom lens apparatus, a wider angle of view and a higher magnification are progressing year by year, the size of a lens disposed in the front portion of the zoom lens device is limited because of the size and weight of the lens.
Therefore, brightness equal to that on the wide-side cannot be kept in the entire zoom area and there occurs the F drop phenomenon that when the zoom portion is driven from a certain position to the tele-side, the brightness of the image field becomes dark in spite of the set value of a quantity of light setting device (aperture) being constant. The F value preferred function is the function of calculating a zoom position at which the F drop phenomenon occurs from the value of the aperture in such a case, limiting the driving range of the tele-side at the calculated zoom position and thereby preventing the occurrence of the F drop phenomenon within the driving range of zoom.
Also, in a large lens used in a TV camera, usually with a view to protect a driving portion, the range of a zoom portion and a focus portion which is narrower than a driving end in mechanism is used as an ordinary driving area. Accordingly, when a zoom position command exceeds a position corresponding to wide-end limit data and tele-end limit data set to avoid being driven to the above-mentioned driving end in mechanism, the zoom position command is limited at a wide-end limit position or a tele-end limit position.
One aspect of the application is to provide a lens apparatus which can perform a proper operation when the lens apparatus having the angle of view correcting function is endowed with the tracking function or the zoom range regulating function such as the F value preferred function.
One aspect of the application is to provide a lens apparatus which can perform the angle of view correcting function as far as possible.
One aspect of the application is to achieve the above object by providing, as a zoom lens apparatus which is provided with a focusing optical portion and a zoom optical portion and in which the range of movement of the zoom optical portion is regulated to a predetermined range, a control circuit having a first mode for setting the movement of the zoom optical portion within the aforementioned regulated range and a second mode for permitting the focusing optical portion to drive a zoom portion beyond the aforementioned regulated range when the fluctuation in angle of view by movement of the focusing optical portion is corrected with the zoom portion movement.
One aspect of the application is to achieve the above objects by providing, in a zoom lens apparatus provided with a focusing optical portion, a zoom optical portion and quantity of light varying means for variably setting the quantity of light passing through the optical portions, a regulating circuit for regulating the range of movement of the zoom portion so that a variation in the quantity of passing light by the movement of the zoom optical portion may not decrease below the set quantity of light, and a control circuit having a first mode for driving the zoom optical portion within the range of movement regulated by the regulating circuit and a second mode for permitting the focusing optical portion to drive the zoom optical portion beyond the range of movement regulated by the regulating circuit when the fluctuation in angle of view by movement of the focusing optical portion is corrected with the zoom portion movement.
One aspect of the application is to achieve the above objects by providing, in a zoom lens apparatus which is provided with a focusing optical portion and a zoom optical portion and in which the movement of the zoom optical portion is regulated to a second movement end inside a first movement end in an area in which the zoom optical portion is movable, a control circuit for permitting the focusing optical portion to drive the zoom optical portion toward the first movement end beyond the second movement end when the fluctuation in angle of view by movement of the focusing optical portion is corrected with the zoom optical portion movement.
Other objects of the present invention will become apparent from the following description of some embodiments of the invention taken in conjunction with the accompanying drawings.